Jack Painter wrote:

"Richard Clark" wrote

So much of this breathless science of rounded tips alludes to the
legitimacy of rare publications equal in scope and stature to those
that announced the proofs of cold fusion.

Did Pons and Fleishman turn their hands to designing Lightning
protection systems to redeem their credentials?

Interested in your comments *after* you have read the study.
http://lightning-protection-institut...-terminals.pdf

Yes, let's have more technical discussion and less name-calling, please.

There seem to be three observations that need to be understood.

1. The electric field gradient near a sharp point is greater than the
field gradient near a blunt point. This is basic physics and should be
completely beyond dispute. But that is the field gradient IMMEDIATELY
LOCAL to the point... and that's not what lightning protection is about.

The whole point of lightning protection is to make a strike attach
specifically to the installed "terminal' and lightning conductor, and
not to any other part of the structure that the installation is aiming
to protect.

So what we want to know is: when a lightning probe leader (the column of
ionized air coming down from the cloud) approaches the structure, how
does the lightning protection terminal attract it from a distance of
many feet away? How does it say "Hey, come over here"?

2. According to Moore et al (the source of the USA Today story that Jack
quoted earlier) a very high field gradient immediately local to tip may
actually be counter-productive, because it can produce corona discharge
which *reduces* the field gradient at a greater distance; and this may
make the probe leader attach somewhere else where there isn't a corona.

At least, that's my reading of Moore's papers (following the trail of
references from the USA Today page, back to the institute in NM where
Moore and colleagues are based). They have a lightning observatory on
top of a mountain, but there only seem to be three short guyed masts
with a different type of terminal on each. Instruments in a small
underground lab collect the data from lightning strikes.

Going back through the paper trail, they have been operating this
facility for more than 10 years, and occasionally produce a paper to one
of the lightning-related journals accompanied by a press release (the
latest of which was picked up by USA Today). However, lightning only
strikes when it feels like it, so the statistical data only build up
very slowly... and if they change the setup on the mountain-top, they'd
effectively have to start again.

Moore's conjecture that you can make the tip of the terminal *too* sharp
is interesting, but his type of "live lightning" experiment doesn't
provide any specific backup for what he's saying. It only produces the
raw observations that he's trying to explain.

Then there is:
3. The paper that Jack quotes above, which reports experiments in a
large 'lightning lab'. The experimental setup is big enough to
investigate effects over a range of several feet, so controlled lab
experiments could bring us a lot closer to the basic physics.

Unfortunately these particular experiments don't seem to help. Same as
with Moore's work, the experiments are heavily biased towards
commercially available lightning terminals which (rather like TV
antennas) come in a variety of weird and wonderful shapes. The
performance of commercial off-the-shelf terminals may be what the
lightning protection industry wants to hear about, but these complex
shapes (with their faint odor of snake oil) make it impossible to
understand what's happening at a basic level.


So it's still wide open for speculation and experiments. Moore's
conjecture - that you *don't* want a corona discharge, so the optimum
tip radius is the one that produces the highest possible field gradient
but *without* inducing corona - looks attractive, but as yet it doesn't
have much theoretical or laboratory backup.

We have to be missing something here in this discussion. There has to be
a whole range of scientific papers, in much more respectable physics
journals that are far removed from the lightning industry, that we're
not aware of.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek